Recently, as demand for miniaturization, weight reduction, and speeding-up of electronic equipment is increased, density growth of the printed wiring board is in progress, and the printed wiring board manufacturing method by a semi-additive process using electroplating receives widespread attention. As described in Japanese Patent Application Laid-Open No. 11-186716, the semi-additive process is a technique in which, after a hole which becomes an interstitial via hole (hereinafter referred to as IVH) is formed by laser or the like in a resin surface on which the circuit is to be formed, an irregularity having roughness of several micrometers is formed by chemical roughening or plasma treatment or the like, on the resin, a Pd catalyst is given, electroless plating having a thickness of about 1 μm is performed, a pattern electroplating resist is formed, a circuit is formed by pattern electroplating, and the resist and the electric power supply layer existing in portions except for the circuit are removed. Compared with a subtractive process that performs large side etching, the semi-additive process allows finer wiring to be formed.
There is also a method in which the circuit is formed on the resin coated metal foil by the semi-additive process. Recently, as described in Japanese Patent Application Laid-Open No. 13-140090 or Japanese Patent Application Laid-Open No. 13-89892, a peelable type metal foil is used in order to decrease a thickness of the metal foil. In the peelable type metal foil, the metal foil having the thickness not more than 5 μm is formed on a support metal foil. In this technique, it is not necessary to perform the electroless plating to the surface of an insulating resin composition layer, so that the printed wiring board having higher reliability can be produced.
In the case where the circuit is formed on the resin coated metal foil by the semi-additive process, as the thinner metal foil becomes more advantageous to the formation of the fine wiring. However, in practice, as described in Japanese Patent No. 2927968, a roughened layer having the thickness of several micrometers for obtaining given peel strength between the metal foil and a resin cured material is provided in the metal foil, which obstructs thinning of the metal foil. In the semi-additive process, it is necessary that the electric power supply layer existing in portions except for the circuit is removed by etching after the electroplating. Because of the irregularity existing in the roughened layer, an etching residue easy to generate, which causes short-circuit failure. Further, because the irregularity of the roughened layer increases electric resistance of a conductor circuit, transmission loss becomes larger. It is known that this increase in electric resistance becomes prominent as a signal is transmitted with higher frequency. When the roughened layer exists in the metal foil, excessive etching is required in forming the conductor circuit, and a conductor top width is narrowed compared to its bottom width, therefore it is not possible to obtain a favorable and fine circuit.
In order to solve the above-described problems, Japanese Patent Application Laid-Open No. 8-309918 discloses a copper clad laminate in which copper foil to which the roughening treatment is not performed and a peroxide curing resin composition which becomes the insulating layer are laminated through a adhesion substrate including a silane coupling agent or a thiol coupling agent. In accordance with the Application, various problems caused by the roughening treatment of the metal foil can be solved without decreasing the peel strength between the copper foil and the insulating layer.
However, in the above-described method, it is necessary to use the peroxide curing resin as the insulating layer. In this case, there is a fear that the reliability of the printed wiring board manufactured with the copper clad laminate including the peroxide curing resin is decreased. Additionally, since the peroxide curing resin itself is potentially hazardous material, handling and retention the material are very difficult and, furthermore, the material is coastlines compared with the insulating resins usually used, so that it is not said that the peroxide curing resin is practical.